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Contact Lubrication

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Contact Lubrication

OVERVIEW
Contact lubricants increase the reliability and lifetime of all current carrying metal interfaces Contact Lubricants Contact lubricants increase the reliability and lifetime of all current carrying metal interfaces. These include switches, connectors and busbars. Electrolube has been the leading supplier of contact lubricants since their invention by Electrolube in the 1950s. A wide range of products is available covering all common applications, while a program of continual development provides specialty products for ever changing customer needs. Manufactured as tenacious greases and oils, products are available for consistent operation at temperature extremes  and with sensitive plastics that are normally attacked by traditional lubricants.

The use of an appropriate contact lubricant will solve the problems of wear, poor signal quality, inconsistent operation and allow the use of less expensive materials. The choice of lubricant can also allow the 'feel' characteristics of the switch to be optimized.

How Contact Lubricants Work Contact technology is constantly developing with new alloys, plastics and customer demands. However, it is still impossible to solve the main cause of switch malfunction i.e. the inability to produce a perfectly smooth metal contact surface. This leads to the following problems:

Heat Generation
Microscopic examination reveals peaks and troughs on the surface and when the contacts come together, only the peaks are actually touching. The true current carrying surface area is therefore far smaller than it would appear. As the current is carried by a fraction of the designed surface area, the heat generated is concentrated at the peaks. This, in turn, causes the formation of high resistance oxide layers. As the resistance increases, more power is converted into heat leading to further oxidation. This spiraling effect creates hot spots reducing the efficiency of the switch and can cause complete failure as the two surfaces weld together.

The application of an Electrolube contact lubricant solves this problem. The lubricant film dramatically increases the effective surface area as, in thin films, the lubricants allow the passage of electricity. The switch now has the surface area that the designers planned. Hot spots are eliminated and the contact resistance remains low and stable.

Arcing
As un-lubricated contacts open and close, arcing (mini-lightning strikes) will occur. Arcing is destructive as it generates heat, causing oxide formation, and as the amount of energy is high, corrosive by-products can be formed. These cause corrosion of the surface and can destroy plated contacts. Ionization of the air and the associated rise in temperature causes metal transfer between the contacts, resulting in the formation of new "peaks and troughs" - a common problem found in high power contacts.

The problem of arcing is compounded in "make & break" switches where every time the circuit is operated, the contacts may bounce several times before finally mating. This exacerbates the problems discussed previously and subjects the circuit to repeated surges of current giving a poor signal to noise ratio.

This problem of arching is not found in lubricated switches, as the lubricant fills the air gap between the contacts, preventing arcing, related temperature rises and corrosive chemical formation. As air is excluded from the metal surfaces, airborne contamination cannot form insulative barriers on the metals. Contact lubricants provide a cushion between the contacts to damp the effects of bouncing.

Mechanical Wear The problems describes previously are compounded by the action of the two surfaces rubbing against each other. This occurs in all metal interfaces, whether static or moving. Why static contacts (connectors) suffer from mechanical wear may not be immediately obvious. However, this phenomenon is explained by the fact that connectors and closed contacts are exposed to small amplitude movements caused by vibration, temperature changes etc. These small movements are known as "frettage". As the surfaces fret, friction causes metal particles to be removed from the peaks breaking through plated surfaces. This exposes surface and underlying metal to the effects of oxidation and wear. Additionally the detached metal particles can cause intermittent signal transmission and ultimately switch failure. The lubricated switch is subjected to far less mechanical wear as the lubricant facilitates smooth movement. Friction is therefore greatly reduced, as is wear, extending switch lifetime. Gold Contacts  Gold contacts are usually thought to be inert but they can also benefit from contact lubrication. While they do not oxidize, gold is porous, so moisture and salts creep under the plated layer which separates from the base metal and is easily worn away. This exposes the base metal which may corrode or oxidize. Contact lubricants form a protective, durable film over the porous areas, preventing the entry of moisture and other contaminants.

Feel Characteristics
The way a switch feels when operated has become an indicator of quality particularly within the automotive industry. Contact lubricants, in addition to their technical benefits can also determine the feel of a switch, whether it be strong and decisive for the dashboard of a commercial vehicle, or smooth and quiet for a luxury car.

Silicone Contamination
Silicone contamination poses particular problems which can also be overcome by contact lubricants. Silicones are found in lubricants, sealants, polishes and mould release agents. As silicones can "creep" great distances, these products should not be used in switch assembly areas. When silicones are present between moving or vibrating contacts, they react under arcing conditions to form silicon carbide. These crystals abrade the contact surface and cause electrical breakdown. Silicone contamination is very difficult to remove, particularly after the formation of silicon carbide. It cannot be removed by solvents. There are certain contact lubricants that can prevent the damage caused by silicones and can even restore damaged contacts. One such treatment from Electrolube reacts with the silicon carbide to form volatile silicon tetrafluoride gas, thus slowly breaking down the hard particles.

If a contact lubricant is used on the switch prior to the introduction of silicones these problems are avoided.

Benefits of Contact Lubrication Contact lubricants are specially formulated greases and oils that reduce friction and enhance the electrical performance of current carrying metal interfaces in switches and connectors. Electrolube products are electrically insulative in thick films, preventing tracking. In ultra thin films, i.e. between closed metal contacts, they allow the current to flow, owing to the "Quantum Tunneling Effect". They also exhibit a neutral pH thereby avoiding surface corrosion.

Tests have shown that contact lubrication can extend the lifetime of switches by more than 300%, producing excellent performance under all circumstances and preventing the need for expensive maintenance. Contact lubricants also help to improve the reputation of manufacturers by reducing or preventing warranty claims and associated commercial costs of product recalls.

The effectiveness of even perfectly designed switches can be improved by contact lubricants and, when considered at design stage, significant production cost savings can be achieved by the use of less expensive materials (both plastics and contact metals).

Typical Applications
Domestic Switches Connectors
The range of applications is vast and can include anything from PC edge connectors to switches in washing machines, kettles, hair dryers and electric blankets. Contact lubricants will bring significant benefits to any application where switches and contacts are fundamental to successful, long term operation.

Automotive Switches Connectors The use of contact lubricants is widespread in the automotive industry, where they are employed to ensure reliability, safety, efficiency and to control the feel of switches.  Common uses include indicators, widows, wipers, horns, ignition, demisters, headlights, locking systems, earthing points and all harness connections. Electrolube contact lubricants also have excellent mechanical lubricity. This allows their use in situations not involving current carrying surfaces, eliminating the potential for failure from the migration of purely mechanical lubricants onto contact surfaces.

Plastic/Plastic Lubrication Electrolube has developed a range of specialty lubricants that offer unrivalled performance by virtue of their high levels of materials compatibility. This allows the use of lower cost plastics including normally sensitive transparent grades (for illuminated fascia switches etc). They are extensively used on rotating shafts within switches, ventilation systems and for the lubrication of plastic cogs and gears.

Electroplating
Electrolube's electroplating compound has been developed to prevent corrosion and contamination', and to improve electrical contact on anode and cathode pick-up shoes, rack contacts and busbar joints.

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